This invention relates generally to drill stem test tools of the type used in oil drilling operations to test potential producing formations and specifically to an improved drag spring unit for well bore drill stem test tools.
Drill stem test (DST) tools are mounted in the drill stem or string and are used to evaluate the producing potential or productivity of an oil or gas bearing zone prior to completing a well. Thus, as drilling proceeds, various indications such as core samples may suggest the desirability of testing a certain formation for producing potential. To conduct the test, an inflatable packer and valve assembly is lowered on the drill stem into the uncased well bore to the zone to be tested. The packer is then set and the valve is opened for flow to the well surface.
Mechanical packers typically utilize a rubber diaphragm which is mechanically deformed outward toward the sides of the well bore by setting weight down on the tool, thereby isolating the zone to be tested. Inflatable packers have distensible members along the tool which are inflated by an integral pump. Rotation of the drill string activates the integral pump thereby pumping fluid to the packers to cause inflation. Inflatable packer type DST tools utilize a drag spring to anchor the lower end of the tool to the sides of the well bore. Rotation of the drill string from the surface while holding the lower end in place actuates the integral pump and inflates the packers.
In the past, one of the most time consuming operations of an inflatable packer drill stem test was removing the drill pipe and tools from the well bore after the test had been run. The normal method of removing drill pipe, other than pipe incorporating an inflatable packer DST tool, involves breaking and threaded connection (tool joint) with the rig tongs and then spinning the rotary table clockwise to unscrew the threads. Clockwise rotation of the rotary table turns the entire amount of drill pipe left in the well bore, along with any tools that are attached to the drill pipe. Since inflatable packer DST tools utilize a pump which is operated by right hand rotation of the rotary table, each time a stand of drill pipe is removed, the pump is turned a few revolutions which gradually pumps the packers up. This is undesirable because it prevents further pipe removal until the packers can be deflated again. It can also result in the packers becoming stuck or damaged.
Because of these problems, drilling crews now use a special procedure to remove drill strings incorporating inflatable packer DST tools. Chain tongs are attached to the stand pipe being removed and the crew walks around the rotary table counterclockwise to unscrew the joint. Although this solves the problem of gradual packer inflation, it is time consuming. Normal operations must be stopped for each stand of pipe being removed so that the chain tongs can be attached and physically walked around the rotary table several times.